Implantable lead and sensor

Abstract

A physiological sensor forms an integral part of an implantable stimulation/sensing lead used with a medical device, such as a pacemaker. The stimulation/sensing lead includes a tip electrode to which a distal end of a first conductor is connected. The sensor is inserted in series with respective portions of a second conductor. A distal end of the second conductor/sensor is connected to the tip electrode. Operation of the stimulation/sensing lead occurs unipolarly through the first conductor only, with a signal return path being provided through the tip electrode and conductive body fluids. The sensor does not form part of the electrical circuit to the tip electrode, and there are no electrical connections or breaks in the insulation along the entire length of the first conductor. Electrical contact with the sensor is achieved during a time window when the stimulation/sensing lead is not being used by applying an appropriate operating signal, and measuring the resultant output signal, at the proximal ends of the first and second leads.

What is claimed is: 
     
       1. An implantable lead and sensor for use with a medical device comprising: a first conductor having a proximal end and a distal end;   first insulation means for electrically insulating said first conductor without interruption along its entire length;   a tip electrode electrically connected to the distal end of said first conductor;   a second conductor having a proximal end and a distal end, the distal end being electrically connected to said tip electrode;   a sensor having first and second terminals to which electrical contact must be made for operation of said sensor, said sensor being electrically inserted in series with said second conductor at a location intermediate the proximal and distal ends of said second conductor, the proximal end of said second conductor being electrically connected to said first sensor terminal, and the distal end of said second conductor being electrically connected to said second sensor terminal; and   second insulation means for electrically insulating said second conductor along its entire length;   said proximal ends of said first and second conductors being adapted for detachable electrical connection with said medical device;   whereby electrical contact is continuously and uninterruptedly maintained with said tip electrode through said first conductor of said lead, thereby assuring impedance stability of said lead in fluid environments; and further   whereby electrical contact may be selectively made with said sensor through the proximal end of said first conductor and the proximal end of said second conductor, the first terminal of said sensor being electrically contacted through the proximal end of said second conductor, and the second terminal of said sensor being electrically contacted through the proximal end of said first conductor by way of an electrical path through said first conductor to said tip electrode and through the distal end of said second conductor to said second sensor terminal.   
     
     
       2. The implantable lead and sensor as set forth in claim 1, wherein said first and second conductors comprise coaxial conductors; said first conductor comprising a first helically wound conductive wire, said first wound wire having a first diameter; said second conductor comprising a second helically wound conductive wire, said second wound wire having a second diameter; said first diameter being less than said second diameter so that said first conductor, including the first insulation means placed thereover, fits inside of the second wound wire. 
     
     
       3. The implantable lead and sensor as set forth in claim 2, wherein said sensor includes passage means therethrough for allowing said first conductor, including said first insulation means, to pass therethrough without interruption. 
     
     
       4. The implantable lead and sensor as set forth in claim 3, wherein said sensor comprises a physiological sensor adapted to sense a physiological parameter of mammalian tissue in which said lead and sensor are implanted. 
     
     
       5. The implantable lead and sensor as set forth in claim 4, wherein said physiological sensor comprises an oxygen sensor adapted to sense optically the oxygen content of blood in optical contact with said sensor. 
     
     
       6. The implantable lead and sensor as set forth in claim 3, wherein said lead comprises a pacemaker lead adapted for use with an implantable pacemaker, said tip electrode being adapted for insertion inside of a mammalian heart. 
     
     
       7. The implantable lead and sensor as set forth in claim 6, wherein said tip electrode is adapted for insertion into a ventricle chamber of said heart, and said sensor is spaced apart sufficiently far from said tip electrode along the length of said lead so as to not reside in said ventricle chamber. 
     
     
       8. The implantable lead and sensor as set forth in claim 7, wherein said sensor is spaced apart from said tip electrode along the length of said lead so as to reside in an atrial chamber of said heart. 
     
     
       9. An implantable lead and sensor combination comprising: a first conductor having a proximal end and a distal end;   first insulation means for electrically insulating said first conductor without interruption along its entire length;   a tip electrode electrically connected to the distal end of said first conductor;   a second conductor having a proximal end and a distal end;   a third conductor having a proximal end and a distal end, the distal end being electrically connected to said tip electrode;   a sensor having first and second terminals to which electrical contact must be made for operation of said sensor, said sensor being electrically inserted in series with said second and third conductors, the distal end of said second conductor being connected to the first sensor terminal and the proximal end of the third conductor being connected to the second sensor terminal; and   second insulation means for electrically insulating said second and third conductors along their entire length;   said proximal ends of said first and second conductors being adapted for detachable electrical connection with a medical device;   whereby electrical contact is continuously and uninterruptedly maintained with said tip electrode through said first conductor, thereby assuring impedance stability of said first conductor in fluid environments; and further   whereby electrical contact may be selectively made with said sensor through the proximal end of said first conductor and the proximal end of said second conductor, the first terminal of said sensor being electrically contacted through the proximal end of said second conductor, and the second terminal of said sensor being electrically contacted through the proximal end of said first conductor by way of an electrical path through said first conductor to said tip electrode and through said third conductor to said second sensor terminal.   
     
     
       10. The implantable lead and sensor as set forth in claim 9, wherein said first, second and third conductors comprise coaxial conductors; said first conductor comprising a first helically wound conductive wire, said first wound wire a first diameter; said second and third conductors each comprising a second helically wound conductive wire, said second wound wire having a second diameter; said first diameter being less than said second diameter so that said first wound wire, including the first insulation means placed thereover, fits inside of the second wound wire of said second conductor and third conductors 
     
     
       11. The implantable lead and sensor as set forth in claim 10, wherein said sensor includes passage means therethrough for allowing said first conductor, including said first insulation means, to pass therethrough without interruption. 
     
     
       12. The implantable lead and sensor as set forth in claim 11, wherein said sensor comprises a physiological sensor adapted to sense a physiological parameter of mammalian tissue in which said lead and sensor are implanted. 
     
     
       13. The implantable lead and sensor as set forth in claim 12, wherein said physiological sensor comprises an oxygen sensor adapted to sense optically the oxygen content of blood in optical contact with said sensor. 
     
     
       14. The implantable lead and sensor as set forth in claim 11, wherein said lead comprises a pacemaker lead adapted for use with an implantable pacemaker, said tip electrode being adapted for insertion inside of a mammalian heart. 
     
     
       15. The implantable lead and sensor as set forth in claim 14, wherein said tip electrode is adapted for insertion into a ventricle chamber of said heart, and said sensor is spaced apart sufficiently far from said tip electrode along the length of said lead so as not reside in said ventricle chamber. 
     
     
       16. The implantable lead and sensor as set forth in claim 15, wherein said sensor is spaced apart from said tip electrode along the length of said lead so as to reside in an atrial chamber of said heart. 
     
     
       17. A method of forming an implantable lead having a physiological sensor as an integral part thereof, said sensor having first and second spaced apart terminals to which electrical contact must be made during its operation, said method comprising the steps of: (a) attaching a first end of a first conductor to a tip electrode, said first conductor having a first length;   (b) insulating said first conductor along said first length without interruption;   (c) attaching a first end of a second conductor to the first terminal of said sensor, said second conductor having a second length that is less than the first length of the first conductor;   (d) insulating said second conductor, including the connection of said second end of said second conductor with said first sensor terminal, along said second length without interruption;   (e) attaching a first end of a third conductor to the second terminal of said sensor, and a second end of said third conductor to said tip electrode, said third conductor having a third length, said second and third lengths, plus the spatial separation of said first and second terminals being approximately equal to said first length of said first conductor;   (f) insulating said third conductor, including the connection of said first end of said third conductor with said second sensor terminal, along said third length without interruption; and   (g) attaching a connector to the first end of said first conductor and the first end of said second conductor, said connector allowing detachable electrical connection to be made to a suitable medical device.   
     
     
       18. The lead forming method as set forth in claim 17, wherein said sensor includes a passage way therethrough, and wherein said method further includes inserting said first conductor, after being insulated along its entire length, through said passage way. 
     
     
       19. The lead forming method as set forth in claim 18, wherein said second and third conductors are formed by helically winding a conductive wire to a prescribed diameter, thereby forming a lumen through the center of said second and third conductors, and wherein said lead forming method further includes inserting said insulted first conductor through said lumen formed in said second and third conductors.